Photo-epilation is known per se; by way of example, reference is made to U.S. Pat. No. 5,735,844. Light originating from a suitable light source (laser; flash lamp) is absorbed by melanin in a hair and/or follicle. The absorbed light is converted into heat. This heat damages or even destroys the follicle. The hair is shed, and new growth is delayed or even fully prevented.
The light is typically applied in pulses. There are several parameters that play a role in epilation efficiency: pulse duration, pulse repetition frequency, wavelength or spectral range of the light, and fluence (or energy density, expressed in J/cm2). When permanent hair removal and thus follicle destruction is intended, literature reports fluences as high as 60 J/cm2 applied in pulses in the range from a few ms to a few hundred ms. U.S. Pat. No. 7,044,959 discloses a method for temporary reduction of hair growth using a broad range of parameter settings for both pulsed sources and continuous sources in scanning motion. In an article “Low dose epilation by alexandrite laser: a dose response study” in Med.Laser Appl., vol. 16, 2001, pp. 293-298, M. Drosner et al. describe a study of hair removal using a relatively low-power alexandrite laser. The wavelength is 890 nm, the fluence is from 5 to 10 J/cm2, the pulse duration is 7 ms. The authors observed long-time hair removal, but they express doubts on the permanency of their method.